KDM6B enhances anti-PD-L1 immunotherapy efficacy by increasing CD8⁺ T-cell infiltration in colorectal cancer

Background: Cytotoxic CD8⁺ T cells play a vital role in its antitumor response, and increasing their infiltration in tumors is an effective strategy for enhancing the efficacy of antitumor immunotherapy. Lysine-specific demethylase 6B (KDM6B) plays a suppressive or oncogenic role in colorectal cancer (CRC). However, the its contribution in CRC immunity remains unclear. Methods: The expression of KDM6B was analyzed in CRC using TCGA database and clinical specimens. Its role in tumor growth and metastasis was assessed through in vitro assays and in vivo models, including subcutaneous xenografts and orthotopic liver metastasis mice. CD8⁺ T cell infiltration, recruitment, and activation were assessed via immunohistochemistry, transwell assay, and flow cytometry. The expression of PD-L1 and CD8⁺ T cell-recruiting chemokines CCL5, CXCL9, CXCL10 were detected. GSEA identified KDM6B-regulated signaling pathways. ChIP‒qPCR was used to determined the enrichment level of H3K27me3 on PD-L1, CCL5, CXCL9, and CXCL10 promoters. Finally, the synergistic effect of KDM6B inducer paricalcitol with anti-PD-L1 therapy was investigated using a subcutaneous xenograft mouse model. Results: KDM6B was downregulated in CRC tissues and cells. KDM6B overexpression suppressed CRC proliferation, tumor growth and liver metastasis, while enhancing CD8⁺ T cells infiltration, recruitment, and functional activation. KDM6B upregulated PD-L1 and CCL5, CXCL9, CXCL1 expression in CRC cells. Mechanically, GSEA revealed JAK/STAT pathway enrichment. KDM6B increased p-STAT3 levels and the STAT3 signaling mediated the promoting effect of KDM6B on PD-L1 and chemokines expression. In addition, KDM6B overexpression reduced H3K27me3 enrichment on promoters of PD-L1 and chemokines. Finally, the combination of paricalcitol and anti-PD-L1 antibody enhanced anti-tumor efficacy in CRC mouse model. Conclusion: KDM6B potentially suppresses CRC progression by enhancing CD8⁺ T cell infiltration via dual mechanisms: STAT3-mediated transcriptional activation and H3K27me3 demethylase-dependent epigenetic remodeling of PD-L1 and chemokine genes (CCL5/CXCL9/CXCL10). The synergistic effect of KDM6B inducer paricalcitol with anti-PD-L1 enhances antitumor immunity, supporting its potential combination strategy for CRC treatment.